Distance estimation using split beam luminaire

ABSTRACT

The invention relates to a method for determining a distance from a sensor to a luminaire. The luminaire includes at least a first light source configured to emit a first light beam adapted to illuminate a predefined area and a second light source configured to emit a second light beam adapted to illuminate a background area surrounding the predefined area. The sensor, which could e.g. be included within another luminaire, is configured to detect a back-reflected first light beam and a back-reflected second light beam. The method includes determining the distance from the sensor to the luminaire based, at least partially, on a comparison of information indicative of a signal strength of the detected back-reflected first light beam and information indicative of a signal strength of the detected back-reflected second light beam.

FIELD OF THE INVENTION

Embodiments of the present invention relate generally to the field ofillumination systems, and, more specifically, to a method and system forestimating distance to a split beam luminaire.

BACKGROUND OF THE INVENTION

As the efficacy (measured in lumen per Watt) and the luminous flux(measured in lumen) of light emitting diodes (LEDs) continues toincrease and prices continue to go down, LED illumination and LED-basedluminaires are becoming viable alternatives to and at a competitivelevel with until now predominant common light bulbs or tube luminescentbased lamps for providing large-area illumination.

By using LEDs it is possible to decrease the energy consumption, arequirement which is well in line with the current environmental trend.Further, as a consequence of having the possibilities to provide brightlight even when using compact LEDs, a number of lighting systems hasbeen proposed greatly differing from the standard lighting systemscomprising a common light bulb. In line with this and by means of usingLEDs instead of light bulbs, a user is also given a more flexiblecontrol of the lighting system illumination functionalities, for examplein relation to intensity dimming control or beam direction.

An example of such a lighting system is disclosed in WO 2011/039690,describing a modular luminaire 100 comprising two light-emittingportions 102 and 104, as shown in FIG. 1. The two portions areindividually controllable and are configured to provide complementarybeam patterns. The portion 102 includes light sources 106 and is adaptedto generate a relatively narrow beam of light illuminating a narrow,task, area. The portion 104 includes light sources 108 and is adapted togenerate a relatively wide, batwing-type beam of light providing ambientillumination of a background area surrounding the task area. Besidesproviding the advantages of a lower cost and a higher comfort level incomparison with conventional office luminaires, such a split beamluminaire enables a local dimming lighting solution with higher energysavings because it allows selectively dimming of lighting fixtures thatare not directly above occupied task areas. However, even with such anadvanced luminaire, it is always desirable to try to reduce energyconsumption even further.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a method is providedfor determining a distance from a sensor to a luminaire. The luminaireis a split beam luminaire comprising at least two light sourcesconfigured to emit light beams with different beam patterns. The firstlight source of the luminaire is configured to emit a first light beamadapted to illuminate a predefined area and the second light source isconfigured to emit a second light beam adapted to illuminate abackground area surrounding the predefined area. The sensor, which coulde.g. be included within another luminaire, is configured to detect aback-reflected first light beam and a back-reflected second light beam.The method includes determining the distance from the sensor to theluminaire based, at least partially, on a comparison of informationindicative of a signal strength of the detected back-reflected firstlight beam and information indicative of a signal strength of thedetected back-reflected second light beam.

As used herein the term “beam pattern” of a light source refers to theintensity distribution of the light source which gives the flux persolid angle in all direction of space.

The first light source may be configured to emit a light beam withrelatively narrow beam pattern (so-called “task beam”), adapted toilluminate a predefined area, e.g. 2×25-2×35 degrees full width halfmaximum (FWHM). This way, the task beam may cover the area that isassociated with a single luminaire in a typical office layout. The beampattern of the task beam is preferably confined within approximately2×50 degrees cut-off angle in order to avoid that the task beam isilluminating the area below a neighboring luminaire.

The second light source may be configured to emit a light beam with arelatively wide beam pattern (so-called “ambient beam”), adapted toilluminate a background area surrounding the predefined area illuminatedwith the task beam. The beam pattern of the ambient beam is preferablyhollow shaped, e.g. a beam pattern with a low intensity at 0 degrees anda peak intensity between 30 and 45 degrees, where, as used herein, theterm “hollow shaped light beam” refers to a beam of light leaving arelatively dark area within the center. The beam pattern of the ambientbeam is preferably used to illuminate a region in between approximately2×20 degrees (in order to have a smooth overlap with the task beam) and2×60 degrees (about 65 degrees is the typical cut-off angle for Europeanoffice luminaires, to avoid indirect glare). In other regions of theworld, the norms on glare are often less strict. For these regions, thepeak intensity and the beam cut-off may be shifted to larger angles.

Further, as used herein, the terms “back-reflected beam of a lightsource,” “back-reflected signals of a light source” and variationsthereof refer to beams which are incident on a sensor not as a result ofthe direct illumination of the sensor by the light source, but as aresult of beams generated by the light source in one main directionbeing reflected in the substantially opposite direction. FIGS. 2A and 2Bschematically illustrate the difference between direct orforward-reflected illumination and back-reflected illumination of asensor. As shown in FIG. 2A, a luminaire 200 installed in the ceiling201 of an office space 202 includes a first light source 203 emitting afirst light beam 204, the task beam, and a second light source 205emitting a second light beam 206, the ambient beam. A sensor 216installed e.g. on the floor or workplane area 207 of the office space202 is directly illuminated by the first light beam 204. The sensor 216is also illuminated by a beam 208 which is a result of the forwardreflection of the second light beam 206 from a point A of e.g. a wall209 or some other object. The reflection at point A is likely to bediffusive, which is shown in FIG. 2A with multiple beams originatingfrom the point A, among which is the beam 208. Of course, the reflectionat point A could also be specular where only the beam 208 would be theresulting forward-reflected beam.

In contrast to FIG. 2A, if the sensor 216 was installed also somewherein the ceiling 201, e.g. if the sensor 216 was included within theluminaire 200, as shown in FIG. 2B, then the sensor 216 would beilluminated by a beam 210, which is a result of the back-reflection ofthe first light beam 204 from e.g. the floor or the workplane area 207and by a beam 212, which is a result of the diffusive back-reflection ofthe second light beam 206 from the point A of. The main direction ofpropagation of the beams 210 and 212 is opposite to that of the maindirection of propagation of the beams 204, 206, and 208. Therefore,beams like the beams 210 and 212 are referred to as “back-reflected”beams.

Embodiments of the present invention are, in part, based on therecognition that optimum dimming levels of the luminaires depend on thedistance between the luminaires present in the structure such as e.g. anopen-plan office. In particular, the optimum dimming levels depend onthe distance between a luminaire and a luminaire in task-lighting mode,i.e. a luminaire at a location where somebody is present. Sinceoperation at optimum dimming levels allows decreasing energy consumptionof the lighting system, it would, therefore, be desirable to be able toestimate distance between the luminaires installed in a particularstructure in an automatic manner and at any time (i.e., dynamically). Tothat end, embodiments of the present invention are further based on therecognition that, when a split beam luminaire is employed, thedifference in the back-reflected signals of the task and ambient beamsof a luminaire, as detected by a sensor preferably included withinanother luminaire, are dependent on the distance from the luminaire tothe sensor (i.e., to the other luminaire, the luminaire comprising thesensor). Specifically, the ratio between the signal strength of thedetected back-reflected ambient light beam, possibly normalized by thelumen output of the ambient beam as described below, and the signalstrength of the detected back-reflected task light beam, possiblynormalized by the lumen output of the task beam, is indicative of thedistance from the sensor to the emitting luminaire. As a result, bycomparing information indicative of the signal strengths of the detectedback-reflected task beam and the detected back-reflected ambient beam itis possible to draw conclusions regarding the distance from the sensorto the luminaire.

In an embodiment, the step of determining the distance from the sensorto the luminaire comprises establishing that the luminaire is aneighboring luminaire with respect to the sensor when the determinedratio is less than 1.1, preferably less than 1.0, most preferably lessthan 0.8, and, otherwise, establishing that the luminaire is along-distance luminaire with respect to the sensor.

In an embodiment, the obtained information regarding the distance fromthe sensor to the luminaire could be used to decrease the energyconsumption of the lighting system by setting the dimming level of theone or more luminaires in a manner that takes into considerationdistance(s) between the luminaires.

While embodiments of the present invention are explained in terms ofcomparing the absolute values of the signal strengths of the detectedback-reflected task and ambient beams (or the derivations of thosevalues), a person skilled in the art will realize that sometimes thosevalues need to be normalized in order to obtain a meaningful comparison.The absolute values of the signal strengths of the detectedback-reflected signals depend on the emitted flux in each beam, which isnot necessarily equal for the task and ambient beams. To account for thedifferences in the emitted flux of each beam it is, therefore,preferably to normalize the detected signal strength of eachback-reflected beam by the lumen output of the light source generatingthat beam. By this normalization, the signal becomes independent of thesettings of the light source. Therefore, in an embodiment, theinformation indicative of the signal strengths of the detectedback-reflected task and ambient beams of the second luminaire isadvantageously determined by normalizing the signal strengths of thedetected back-reflected task and ambient beams of the second luminairewith respect to the lumen output of the light sources generating each ofthe respective beams.

In an embodiment, to obtain different beam patterns from the first andsecond light sources, each light source may include a light emitter,such as e.g. one or more light emitting elements such as LEDs, and anassociated beam shaping optics. Possible materials that could be usedfor the LEDs include inorganic semiconductors, such as e.g. GaN, InGaN,GaAs, AlGaAs, or organic semiconductors, such as e.g. small-moleculesemiconductors based on Alq3 or polymer semiconductors based e.g. on thederivatives of poly(p-phenylene vinylene) and polyfluorene. Theassociated beam shaping optics could include appropriately designedlens, TIR (total internal reflection) collimator, or metallic reflector.The beam shaping optics may be configured to generate a beam of aspecific width/pattern. For example, for the first light sourceconfigured to generate a task beam, the beam shaping optics may bedesigned to generate a beam corresponding to the size of an office deskor corresponding to the area defined by the typical luminaire spacing intwo directions (the latter is particularly advantageous forimplementations where it is not known where the desks would be withrespect to the luminaires). For the second light source configured togenerate an ambient beam, the beam shaping optics may be designed togenerate a beam with a relatively low intensity part corresponding tothe shape of the task beams and adapted to illuminate the surroundingbackground area. In this manner, the first and second light sources maybe adapted to e.g. provide complementary beam patterns to obtain asmooth total beam pattern for the luminaire.

Further, the emission of the first light source is preferably controlledindependently from emission of the second light source, in order toallow for different illumination levels at the task area and at thebackground area surrounding the task area. As described above, thehollow shaped beam pattern provided by the second light source may begenerated using at least one light emitting element and associated beamshaping optics designed to create a hollow beam shape. Alternatively,the second beam of light may be generated using a first and a secondlight emitting elements of the second light source, the first and secondlight emitting elements of the second light source being separatelycontrollable with respect to the light emitting element(s) of the firstlight source, each of the first and second light emitting elements ofthe second light source configured to generate complementary beampatterns together configured to create the hollow shaped beam pattern.

In an embodiment, the first light beam may include first data encodedtherein and the second light beam may include second data encodedtherein, the data being encoded in any of the conventional manners forencoding data into luminance output of a light source, such as e.g.described in WO2006/111930 or WO2008/050294. In one further embodiment,the first and second data may include data that at least allows thesensor to distinguish between detected back-reflected beams of the firstand second light sources and/or that allows a unique identification ofthe light source that generated the beam. In other embodiments,additional information could be encoded in each of the beams, such ase.g. a lumen output generated by the respective light source, driversettings of the light source, and/or any other information which may berelated to the light source.

According to other aspects of the present invention, a controller forimplementing the above method and various luminaires for use with theabove method and/or the controller are also disclosed. Also, the presentdisclosure relates to a computer program with portions, possiblydistributed, for performing the various functions described herein andto a data carrier for such software portions.

According to yet another aspect of the present invention, a lightingsystem for a structure, such as e.g. an office space, is provided. Thelighting system includes a system control unit and a plurality ofluminaires. Each luminaire includes a first light source configured foremitting a first light beam adapted to illuminate a predefined area, asecond light source configured for emitting a second light beam adaptedto illuminate a background area surrounding the predefined area, asensor configured for detecting at least a back-reflected first lightbeam and a back-reflected second light beam of another luminaire, and aninterface configured for providing to the system control unitinformation indicative of a signal strength of the detectedback-reflected first light beam and information indicative of a signalstrength of the detected back-reflected second light beam of the otherluminaire. The system control unit is configured for acquiringinformation detected by the sensors of at least some of the plurality ofluminaires, determining distance between at least two luminaires of theplurality of the luminaires based, at least partially, on the acquiredinformation, and controlling the first light source and/or the secondlight source of at least some of the plurality of luminaires based, atleast partially, on the determined distance(s). The system control unitmay also acquire a task and background area lighting level configurationfor the structure, and control the first and second light sources of atleast some of the plurality of luminaires such that a total illuminationpattern produced by the plurality of luminaires corresponds to the taskand background area lighting level configuration for the structure. Inthis manner, a centralized management of the luminaires may be achieved.

Hereinafter, an embodiment of the invention will be described in furtherdetail. It should be appreciated, however, that this embodiment may notbe construed as limiting the scope of protection for the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

In all figures, the dimensions as sketched are for illustration only anddo not reflect the true dimensions or ratios. All figures are schematicand not to scale. In particular the thicknesses are exaggerated inrelation to the other dimensions. In addition, details such as LED chip,wires, substrate, housing, etc. have sometimes been omitted from thedrawings for clarity.

FIG. 1 illustrates a modular split beam luminaire according to priorart;

FIG. 2A illustrates a sensor being illuminated by direct andforward-reflected beams;

FIG. 2B illustrates a sensor being illuminated by back-reflected beams;

FIG. 3 illustrates an illumination system comprising a plurality ofluminaires according to one embodiment of the present invention;

FIG. 4 is a block diagram of an illumination system, according to oneembodiment of the present invention;

FIG. 5 illustrates a light distribution of an exemplary split beamluminaire in an open-plan office, according to one embodiment of thepresent invention;

FIG. 6 illustrates a comparison of light distributions of direct orforward-reflected beams of an exemplary split beam luminaire placed inan open-plan office, in a cell office, and in a corridor, according toone embodiment of the present invention;

FIG. 7 illustrates a comparison of light distributions of back-reflectedbeams of an exemplary split beam luminaire placed in an open-planoffice, in a cell office, and in a corridor, according to one embodimentof the present invention;

FIG. 8 illustrates the ratio of the signal strengths of back-reflectedambient beam and task beam vs distance for the open-plan office,according to one embodiment of the present invention; and

FIG. 9 illustrates the ratio of the signal strengths of back-reflectedambient beam and task beam vs distance for the cell office, according toone embodiment of the present invention.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth toprovide a more thorough understanding of the present invention. However,it will be apparent to one of skill in the art that the presentinvention may be practiced without one or more of these specificdetails. In other instances, well-known features have not been describedin order to avoid obscuring the present invention.

FIG. 3 shows a structure 300—in this case a room—with an installedillumination system 310. The illumination system 310 comprises one ormore of luminaires 320 and one or more controllers (not shown in FIG. 3)controlling the luminaires 320. The illumination system 310 may furthercomprise a remote control 330 allowing a user to control the lightsources 320. While FIG. 3 shows that each of the luminaires 320 generatea single beam, this is merely a schematic illustration intended to showthat the luminaires 320 are used to provide illumination of thestructure 300, while, as described below, each of the luminaires 320 is,preferably, a split-beam luminaire generating two light beams withdifferent beam patterns.

FIG. 4 is a schematic illustration of an illumination system 400according to one embodiment of the present invention. The illuminationsystem 400 may be used as the illumination system 310 in the structure300 illustrated in FIG. 3. As shown, the illumination system 400includes at least one split beam luminaire 420 comprising at least afirst light source 422, a second light source 424, and a sensor 426 andconfigured to generate light according to light settings. Theillumination system 400 further includes a luminaire control unit 410configured to control the luminaire 420. In addition, the illuminationsystem 400 includes a controller 430 for at least determining presenceof objects in the surrounding of the luminaire 420 and/or determiningdistance from the luminaire 420 to other luminaires in the illuminationsystem 400.

Each of the luminaire control unit 410 and the controller 430 mayinclude a microprocessor, microcontroller, programmable digital signalprocessor or another programmable device. They may also, or instead,include an application specific integrated circuit, a programmable gatearray or programmable array logic, a programmable logic device, or adigital signal processor. Where the luminaire control unit 410 or thecontroller 430 includes a programmable device such as themicroprocessor, microcontroller or programmable digital signal processormentioned above, the processor may further include computer executablecode that controls operation of the programmable device. Additionally,the luminaire control unit 410 and/or the controller 430 may be equippedwith communication circuitry for allowing remote control of the lightinglevel configuration using e.g. the remote control 330 and/or with memoryfor storing data.

In other embodiments, the illumination system 400 may include additionalluminaires and additional luminaire control units controlling theadditional luminaires. For example, the illumination system 400 mayfurther include a second split beam luminaire 440 which can include atleast a first light source 442 and a second light source 444, and,optionally, also a sensor 446, similar to the sensor 426. Suchembodiments will be described herein with a reference to a singleluminaire control unit (the system luminaire control unit 410)controlling the various luminaires. However, people skilled in the artwill recognize that the system luminaire control unit 410 may compriseindividual controllers for each of the luminaires included in theillumination system 400, possibly with one such luminaire control unitincluded within each luminaire. Similarly, embodiments are describedherein with a reference to a single controller 430 determining presenceof objects for all of the luminaires included in the illumination system400, in other embodiments, an individual controller such as thecontroller 430 could be associated with, and possibly included within,each one of the luminaires.

The operation of the luminaire 420 will now be described in greaterdetail. The operation of the second luminaire 440 is substantially thesame as the operation of the luminaire 420 and, therefore, in theinterests of brevity, its description is not repeated here.

The light sources 422 and 424 of the luminaire 420 are configured toemit light beams with different beam patterns. To that end, each of thelight sources 422 and 424 may include one or more light emittingelements such as e.g. one or more LEDs (not shown in FIG. 4) andassociated beam shaping optics (also not shown in FIG. 4) enabling thelight sources 422 and 424 to provide light beams with differentpredetermined beam patterns. As discussed above, the first light source422 is configured to provide a task beam with a relatively narrow beampattern with e.g. 2×25 degrees FWHM, while the second light source 424is configured to provide an ambient beam with an in comparison broader,preferably hollow, beam pattern, e.g. a beam with a hollow center andpeak intensity between 30 and 40 degrees. In one embodiment, thecorresponding beam shaping optics for the light sources 422 and 424 mayinclude appropriately designed lenses that could be manufactured by e.g.injection molding in the form of a plate containing an array of suchlenses. In alternative embodiments, the beam-shaping optics couldinclude e.g. TIR collimators or metallic reflectors.

The sensor 426 of the luminaire 420 could be any conventional lightsensor, preferably a broad-angle light sensor, comprising aphotodetector and, possibly, a processing unit, adapted for detectingand being able to differentiate between back-reflected signals of thetask and ambient beams generated by the light sources 422 and 424. Inaddition, the sensor 426 may further be adapted for detecting and beingable to differentiate between the back-reflected task and ambient beamsgenerated by the light sources of luminaires other than the luminaire420 that the sensor 426 is included in, such as e.g. the beams generatedby the light sources 442 and 444 of the luminaire 440. In an embodiment,in addition to having a broad-angle light sensor, the sensor 426 couldinclude also a second, presence, sensor (not shown in FIG. 4), e.g. apassive infrared (PIR) or ultrasonic presence sensor, having a detectioncone substantially overlapping with the task beam of the light source422 (i.e., the narrow-angle sensor). Such an embodiment could beadvantageous for detecting presence in the area illuminated by the taskbeam. Functionality of the sensor 426 relevant for the embodiments ofthe present invention is discussed in greater detail below.

Persons skilled in the art will realize that, even though the sensor 426is shown in FIG. 4 to be included within the luminaire 420, in otherembodiments, the sensor 426 may be implemented separately from theluminaire 420, as long as it is still able to detect the back-reflectedtask and ambient beams generated by the luminaire 420 at substantiallythe same signal strengths as if it was included within the luminaire.That means that the sensor 420 could be installed in the vicinity of theluminaire 420 so that the difference in the detected signals strengthsof the back-reflected signals between such a sensor and a similar sensorincluded within the luminaire would be negligible.

The illumination system 400 is configured to operate as follows. Asshown in FIG. 4, the light settings for the illumination system 400 areprovided to a drive signal generator 450 (which, optionally, may beincluded within the illumination system 400). The light settingsindicate what the average lumen output of each of the two light sourcesof each of the luminaires 420 and 440 should be in terms, for example,of light power, e.g. defined in lumen, and color. The light settings maybe provided by a user via the remote control 330 or may be preprogrammedand provided from an external unit controlling the scene setting.Alternatively, the light settings may be preprogrammed and stored in amemory within the drive signal generator 450 or within the illuminationsystem 400. The drive signal generator 450 translates the light settingsinto different electrical drive signals for different light sourceswithin the illumination system 400 and provides the drive signals to thesystem luminaire control unit 410. The drive signals, in turn, controlthe dimming levels of the different light sources within each of theluminaires of the illumination system 400. For a constant dimming levelper light source, the drive signal that is provided from the drivesignal generator 450 to the system luminaire control unit 410 comprisesa repeated pattern of pulses, a so-called “drive pattern,” repeatingwith a certain frame period. Various methods for dimming the lightsources are known to people skilled in the art and, therefore, are notdescribed here in detail. These methods include e.g. pulse widthmodulation, pulse density modulation, or amplitude modulation.

In one embodiment, the system luminaire control unit 410 may further beconfigured to receive a data signal 465 from a data source 460. The datasignal 465 includes data that the system luminaire control unit 410could be configured to embed into at least some of the light beamsgenerated by the light sources of the luminaires in the illuminationsystem 400. The data may represent, for example, a localizedidentification of the illumination system 400, the luminaire 420 and/orit's light sources 422 and 424, their capabilities and current lightsettings, or other type of information that may be related to theillumination system 400. Alternatively or additionally, the data that isintended to be embedded into the light beams may be pre-stored withinthe illumination system 400, e.g. stored in the system luminaire controlunit 410, and/or obtained from sources other than the data source 460,e.g. from the controller 430.

The system luminaire control unit 410 is then configured to embed thedata into at least some light beams generated by the light sources bymodulating drive signals applied to those light sources. Various methodsfor embedding data into the lumen output of the light sources are knownto people skilled in the art and, therefore, are not described here indetail.

FIG. 5 illustrates a light distribution of an exemplary split beamluminaire in an open-plan office, according to one embodiment of thepresent invention. The split beam luminaire could e.g. be the luminaire420 described above, which could be one of the luminaires 320illustrated in FIG. 3, while the office could be the structure 300. Asused herein, the term “open-plan office” refers to a space that isrelatively wide open, where a luminaire could be considered to beinstalled so that there are no walls or high cupboards in itssurrounding, as would be present in a “cell office” (i.e., an officespace separated into cubicles) or in a relatively narrow corridor.

The horizontal axis of FIG. 5 illustrates position in meters, where theblocks 520 illustrate luminaires such as e.g. luminaires 320 illustratedin FIG. 3, where each of the luminaires 520 could be the luminaire 420described above. The vertical axis of FIG. 5 illustrates the detectedlight beams (lux level) on a logarithmic scale.

In FIG. 5, only the third luminaire from the left of all the luminaires520 is emitting light. Considering that the emitting luminaire is theluminaire 420, this means that the light source 422 is generating a taskbeam and the light source 424 is generating an ambient beam.

Curves 502 and 504 illustrate signal strengths of the task beam and theambient beam, respectively, as detected by a lux sensor at a workplaneheight where the sensor is illuminated by direct and/orforward-reflected task and ambient beams generated by the light sources422 and 424, respectively. As is clearly seen from the comparison of thecurves 502 and 504, the task beam (curve 502) is more localized than theambient beam (curve 504).

Curves 512 and 514 illustrate signal strengths of the back-reflectedtask and ambient beams, as detected by a lux sensor at the ceiling, suchas the sensor 426 included in the emitting luminaire. The differencebetween the back-reflected signals of the task and ambient beamsillustrated with curves 512 and 514 is less distinct than for curves 502and 504, where the direct illumination has the dominant contribution,but there is still a clear difference in the signal strength of thedetected back-reflected task and ambient beams when measured by a sensorincluded in the emitting luminaire.

Each of FIGS. 6 and 7 illustrates a comparison of light distributions(lux levels normalized to the lumen output of the source) of anexemplary split beam luminaire placed in different structures comprisingan open-plan office, a cell office, and a corridor, according to oneembodiment of the present invention. Again, the split beam luminairecould e.g. be the luminaire 420 described above, which could be one ofthe luminaires 320 illustrated in FIG. 3, while each of the differentstructures could be the structure 300. To obtain the light distributionsof FIGS. 6 and 7, the open-plan office considered was a spacious openoffice with a luminaire installed in the center so that there aresubstantially no objects in the area surrounding the luminaire, the celloffice was a 3.6×5.4 meters (m) cell office, and the corridor was acorridor of 2 m width. The open-plan office, the cell office, and thecorridor differ in the presence of walls that would be in thesurrounding of an emitting luminaire, with the open-plan office havingthe least, if any, of objects such as walls in the surrounding of aluminaire, the cell office having more objects (walls) in thesurrounding of a luminaire, and the corridor having the most objects(walls) in the surrounding of a luminaire.

In FIGS. 6 and 7, each of the curves 612 and 712 represent a lightdistribution of a task beam generated by the light source 422 in theopen-plan office, each of the curves 614 and 714 represent a lightdistribution of an ambient beam generated by the light source 424 in theopen-plan office, each of the curves 622 and 722 represent a lightdistribution of a task beam generated by the light source 422 in thecell office, each of the curves 624 and 724 represent a lightdistribution of an ambient beam generated by the light source 424 in thecell office, each of the curves 632 and 732 represent a lightdistribution of a task beam generated by the light source 422 in thecorridor, and each of the curves 634 and 734 represent a lightdistribution of an ambient beam generated by the light source 424 in thecorridor. FIG. 6 illustrates the light distribution as measured by asensor detecting direct and/or forward-reflected light beams, e.g. asensor placed on the floor or at the workplane area of the structure,while FIG. 7 illustrates the light distribution as detected by a sensordetecting the back-reflected light beams, e.g. a sensor integrated inthe ceiling of the structure.

In both FIG. 6 and FIG. 7, the horizontal axis illustrates the positionin the plane of measurement (i.e. either the floor/workplane plane ofmeasurement or the ceiling plane) of the sensor detecting lumen output,measured in millimeters (mm), while the vertical axis illustrates thedetected illuminance by the light beams (measured in lux) normalizedwith respect to the lumen output of the light beams generated by therespective light source, measured in lumens (lm). For both figures, theemitting luminaire 420 is located at the position of 1200 mm. Therefore,in both figures, position 1200 mm is also where the detected luminancelevels are highest. This means that when the sensor 426 is includedwithin or substantially near the emitting luminaire 420 (i.e. it detectsthe back-reflected signals, FIG. 7) at the position of 1200 mm, such asensor will detect the highest values of signals generated by theluminaire 420, the values that could be obtained at the crossing of eachof the curves 712, 714, 722, 724, 732, and 734 with a vertical dashedline 701 indicating the position of 1200 mm.

Since this distribution shown in FIG. 6 is mainly determined by directillumination, the effect of the walls is very small, which can be seenfrom the analysis of the curves 612, 614, 622, 624, 632, and 634. Thus,FIG. 6 illustrates that the presence of a wall is not easy to deductfrom the direct/forward-reflected illumination profile. In contrast,when the light sensor is integrated in the luminaire, i.e. it senses theback-reflected light at level of the luminaire, two effects induced bythe presence of a wall may be observed in the light distributiondetected by such a sensor, as shown in FIG. 7. Again, for the sensorintegrated within the emitting luminaire, illuminance values at thecrossing of each of the curves 712, 714, 722, 724, 732, and 734 with avertical dashed line 701 in FIG. 7 should be considered.

The first effect that can be observed from analyzing the lightdistributions of FIG. 7 is that the signal strength of theback-reflected beam (for both, the task and the ambient beams) increasesas more objects are placed in the surrounding of the luminaire. For thetask beam, this can be seen by comparing the curves 712, 722, and 732.As shown in FIG. 7, the signal strength of the back-reflected task beamin the corridor (i.e., the “most objects” situation), illustrated withthe curve 732, is greater than the signal strength of the back-reflectedtask beam in the cell-office (i.e., “less objects than in the corridor”situation), illustrated with the curve 722, which, in turn, is greaterthan the signal strength of the back-reflected task beam in theopen-plan office (i.e., the “no objects” situation), illustrated withthe curve 712. This effect on its own could be used to deriveinformation regarding presence of objects in the surrounding of theluminaire. However, this should be done with caution as the signalstrength on its own may not be a very reliable trigger because thissignal strength may be influenced by many factors, such as the wallpaint, floor covering, furniture, etc.

The second effect, however, can be used as a relatively robust triggerfor the presence of a wall or at least a very large vertical object. Thesecond effect induced by the presence of walls is that the relativestrengths of the back-reflected task light beam and the back-reflectedambient light change order. As shown in FIG. 7, in the open-plan officewith no walls in the surrounding of the emitting luminaire, the signalstrength of the back-reflected task beam (curve 712) is greater than thesignal strength of the back-reflected ambient beam (curve 714). Thisrelation changes to the opposite when there are walls in the surroundingof the luminaire, as can be seen for the cell office and corridor curvesof FIG. 7. As shown in FIG. 7, in the cell office with some walls orother objects in the surrounding of the emitting luminaire, the signalstrength of the back-reflected ambient beam (curve 724) becomes greaterthan the signal strength of the back-reflected task beam (curve 722). Inthe corridor with even more walls or other large vertical objects in thesurrounding of the emitting luminaire, this effect is even morepronounced. Like for the cell office, the signal strength of theback-reflected ambient beam in the corridor (curve 734) is also greaterthan the signal strength of the back-reflected task beam (curve 732),with the difference between signal strengths of the back-reflectedambient and task beams being greater for the corridor (i.e. thedifference between curves 734 and 732) than for the cell office (i.e.the difference between curves 724 and 722). The effect of the signalstrength of the back-reflected ambient beam becoming greater than thesignal strength of the back-reflected task beam may be explained by thefact that, due to the presence of a wall, the back-reflection of ambientlight is stronger than that of task light, whereas in the open space theback-reflection of task light is stronger. As the foregoing illustrates,the second effect may be used to determine presence of objects, inparticular, relatively large vertical objects in the surrounding of theemitting luminaire. To that end, returning to the luminaire 420illustrated in FIG. 4, the sensor 426 could detect the back-reflectedbeams of the task and ambient beams generated by the light sources 422and 424, respectively, and provide the values of the detected signalstrengths or derivations thereof to the controller 430, possibly aftersome processing in the processing unit of the sensor 426.

There are various manners of how the sensor 426 could be configured todifferentiate between the back-reflected task beam and theback-reflected ambient beam generated by the luminaire 420. In apreferred embodiment, the sensor 426 may be configured to make such adifferentiation based on an identification of the light source encodedin each of the task beam and the ambient beam, as described above.However, there are many other ways for the sensor 426 to make such adifferentiation that would be known to a person skilled in the art and,therefore, are intended to be within the scope of the present invention.For example, the sensor 426 can differentiate between the back-reflectedtask and ambient beams because the task and ambient beams are beams ofdifferent spectral compositions. Additionally or alternatively, thelight sources 422 and 424 could be configured to emit their respectivebeams sequentially (i.e., not at the same time) and the sensor 426 couldbe synchronized with such emission, so that the sensor 426 would be ableto differentiate between the detected back-reflected signals.

The controller 430 includes at least an interface for receiving datafrom the sensor 426 as well as, optionally, from other entities such ase.g. the drive signal generator 450, a processing unit for processingdata, and, possibly, a memory for storing data (the interface, theprocessing unit, and the optional memory of the controller 430 are notshown in FIG. 4). The controller 430 may process the values receivedfrom the sensor 426 further by e.g. normalizing the signal strengthsmeasured by the sensor 426 with respect to the lumen output, or someinformation indicative of the lumen output, such as e.g. driversettings, of the beams generated by the light sources of the luminaire420. In one embodiment, the controller 430 may obtain informationindicative of the lumen output of the beams generated by each of thelight sources 422 and 424 because that information is e.g. encoded inthe light beams produced by the light sources. In another embodiment,information regarding the lumen output could be provided to thecontroller 430 by the luminaire control unit 410 or may bepre-programmed in the controller 430. Alternatively to the controller430 performing the processing of data measured by the sensor 426, suchprocessing could also similarly be done within the sensor 426 if thesensor 426 is equipped with some kind of a processing unit, as sensorstypically are equipped with. Of course, the information indicative ofthe detected signal strengths could also be processed both in the sensor426 and in the controller 430.

The processing unit of the controller 430 may then be configured todetermine whether objects are present in the area surrounding theluminaire 420 based on the comparison of the information indicative ofthe signal strengths of the detected back-reflected task and ambientbeams. The processing unit of the controller 430 may be configured toestablish that one or more objects are present in the surrounding of theluminaire 420 if the signal strength (or a derivation thereof) of thedetected back-reflected ambient beam is greater than the signal strengthof the detected back-reflected task beam and, otherwise, to establishthat no such objects are present.

As discussed previously herein, the optimum dimming levels of the lightsources of a split beam luminaire depend strongly on the type of spacethat needs to be illuminated, or, in other words, on the presence ofobjects in the area surrounding the luminaire. In a regular small celloffice, the required dimming levels are typically about 20% higher thanin an open space office, in order to guarantee a task lighting level ofat least 500 lux. At least partially, this is caused by light absorptionat the walls of the small office where, typically, an absorption of 50%may be assumed for the walls. In larger offices, however, these lossescan be neglected. Furthermore, the relative dimming levels of the taskand ambient beams of the luminaire may also be different in a celloffice depending on the required light effect. For improved energysaving, it may be advantageous to reduce the ambient beam with respectto the task beam, such that the light loss at the wall may be reduced.For improved visual comfort, however, the ambient light beam at thewalls could be increased with respect to the task light, since the lightlevel perception in a room is dominated by the vertical illuminance ofwalls and cupboards and not by horizontal illuminance of task areas. Inany case, the dimming levels of a split beam luminaire located close toa wall should preferably differ from the dimming levels of the sameluminaire in the middle of a large office. Therefore, the controller 430may then be configured to provide an instruction to the luminairecontrol unit 410 to adjust the dimming level(s) of the first and/orsecond light sources of the luminaire 420 in accordance with thedetermination of whether or not objects are present in the areasurrounding the luminaire 420. For example, when the controller 430determines that objects are present in the area surrounding theluminaire 420, the dimming levels of the task and ambient beams may beadjusted to a “wall-mode,” as described above.

In an embodiment, in addition to or instead of enabling thedetermination of object presence in the surrounding of the luminaire 420by detecting the back-reflected task and ambient beams generated by theluminaire 420, the sensor 426 may be used to enable the estimation ofdistance from the luminaire 420 to another luminaire within theillumination system 400, e.g. the second luminaire 440.

As described above, the second luminaire 440 includes at least the firstlight source 442 and the second light source 444 configured to emit taskand ambient light beams, respectively, similar to the light sources 422and 424 described above. The sensor 426 of the first luminaire 420 maythen be configured to detect the back-reflected task and ambient beamsgenerated by the light sources of the second luminaire 440. To that end,the sensor 426 may be configured to differentiate between the detectedback-reflected task and ambient beams of the second luminaire 440 in oneof the manners described above for differentiating between the differentbeams of the first luminaire 420. Again, in a preferred embodiment, thedifferentiation would be done based on the unique identification codesincluded in the task and ambient light beams generated by the secondluminaire 440.

The sensor 426 would then provide the detected values to the controller430, possibly with some processing of the values, as described above forthe signals detected from the luminaire 420, which would compare theinformation indicative of the signal strengths of the detectedback-reflected task and ambient beams of the second luminaire toestimate the distance from the sensor 426 to the second luminaire 440.When the sensor 426 is included within or substantially near theluminaire 420, the estimated distance would also be the distance betweenthe luminaires 420 and 440.

To understand better how it is possible to estimate the distance in thismanner, FIG. 7 could be considered again. As described above, thehorizontal axis of FIG. 7 illustrates position of the sensor measuringthe signals, and for determination of presence in the surrounding of theluminaire, the luminance values detected along the dashed line 701 wereconsidered. Now, considering that the emitting luminaire, the luminaire440, is still positioned at the position 1200 mm on FIG. 7, a sensorlocated at e.g. position −1200 mm would detect the values along a dashedline 702. As can be seen from comparing the values of the six curvesillustrated in FIG. 7 for different positions of the sensor in the planeof measurement, particularly from comparing the values along the line701 and the values along the line 702, the difference between thedetected back-reflected task and ambient beams of an emitting luminaireis decreasing as the sensor is positioned further and further away fromthe emitting luminaire. This effect can be used to determine thedistance from the luminaire in which sensor is taking measurements ofthe back-reflected task and ambient beams of the other luminaire to theother luminaire that's actually generating the task and ambient beamsbeing measured.

FIG. 8 illustrates the ratio of the signal strengths of back-reflectedambient beam and task beam vs distance for the open-plan office. Asshown with curve 801 in FIG. 8, the ratio is smallest at the location ofthe emitting luminaire (i.e., at the position 1200 mm), and thenincreases with distance. In view of that, the controller 430 could bee.g. configured with a predetermined cutoff value for the ratio of whenthe luminaire comprising the sensor that's detecting back-reflectedsignals from the other luminaire can be considered to be nearestneighbor for the other luminaire. For example, based on the measurementsof the back-reflected signals taken by the sensor 426 of the firstluminaire 420, the controller 430 could be configured to determine theratio and then indicate that the second luminaire 440 is the nearestneighbor to the luminaire 420 if the determined ratio is less than 1.1,preferably less than 1.0, and most preferably less than 0.8. If theratio was greater than that predetermined value, the second luminaire440 would be considered to be a long distance luminaire with respect tothe luminaire 420.

Alternatively or additionally, the controller 430 could be provided witha look-up table containing different ratio values and correspondingdistances between luminaires and be configured to determine the distancebased on comparing normalized signal strengths of the back-reflectedtask and ambient beams of the second luminaire (i.e., determining theratio) and then looking up the value for the distance corresponding tothis ratio.

In an embodiment, in addition to determining the distance to the secondluminaire based on the comparison of normalized signal strengths of theback-reflected task and ambient beams of the second luminaire, thecontroller 430 may have access to additional information that may beused to determine accuracy of the determined distance, correct thedetermined distance, and/or supplement the determination of thedistance. For example, the sensor 446 of the second luminaire 440 couldbe configured to detect the relative signal strengths of theback-reflected signals of the task and ambient beams generated by thesecond luminaire 440 (i.e., the values at position 1200 in FIG. 7) andthen the detected relative signal strengths may either be encoded in thelight beams generated by the luminaire 440 or provided to the controller430 in some other manner. The controller 430 could then be configured tocompare the relative signal strengths of the ambient and task beams ofthe second luminaire 440 as detected by the sensor 426 of the firstluminaire 420 with the local signal strengths at the emitting source(i.e., the values provided from the measurements at the luminaire 440)to obtain information indicative of the reduction in signal strength ofthe light beams generated by the second luminaire. The controller 430could then use the obtained information regarding the reduction insignal strength to supplement the determination of the distance betweenthe first luminaire 420 and the second luminaire 440 or to check and/orcorrect the distance determined based on the comparison of theback-reflected task and ambient beams of the second luminaire asdetected by the sensor of the first luminaire. In this manner, thecontroller 430 could have three inputs for determining the distance tothe second, emitting, luminaire: ratio of back-reflected task andambient signals as detected by the sensor in the first luminaire,decrease in back-reflected task signal from the value detected by thesensor in the second luminaire to the value detected by the sensor inthe first luminaire, and decrease in back-reflected ambient signal fromthe value detected by the sensor in the second luminaire to the valuedetected by the sensor in the first luminaire.

FIG. 9 illustrates the ratio of the signal strengths of back-reflectedambient beams and task beam vs distance for the cell office. Comparedwith the curve 801 of FIG. 8, as shown with curve 901 in FIG. 9, in thecell-office the ratio stays roughly the same and provides lessinformation about distance. But, since the cell-office considered wassmall anyway, there is no need to estimate distance because in such asmall office all luminaires could be considered to be nearest neighbors.

Based on the estimated distance between the luminaires, the controller430 may then be configured to provide an instruction to the luminairecontrol unit 410 to adjust the dimming level(s) of the first and/orsecond light sources of the luminaire 420 and/or of the luminaire 440,depending on the distance between these luminaires. As a result, theluminaires close to the task lighting luminaire, i.e. close to thesitting person, can be set to e.g. a 300 lux ambient light setting,whereas the luminaires far from that person may be set to an even lowerlight level, like 100 lux.

Adjusting the dimming levels of the luminaires based on the distancebetween them allows saving additional energy in the illumination system400 by avoiding overshoot. When all luminaires are in task lightingmode, the general light level is higher than 500 lux because this isneeded to guarantee a 500 lux task level below an isolated taskluminaire when all other luminaires are in the ambient mode. Theovershoot of about 10-20% is, therefore, needed to compensate for thereduced light level at the task area by the dimmed neighboringluminaires. When a sufficient number of neighboring luminaires are intask lighting mode, the overshoot is not needed and the task lightingluminaire may dim down by 10-20%. This may be sensed by counting thenumber of task lighting signals and estimating their distance by themethod described above for creating zones.

While the controller 430 has been illustrated in FIG. 4 as a unitseparate from the luminaire control unit 410 and the luminaire 420, inother embodiments, functionality of the controller 430 and the luminairecontrol unit 410 could be combined in a single unit or, conversely,distributed over a greater number of controllers. Further, the luminairecontrol unit 410 and/or the controller 430 could be included within theluminaire 420.

The embodiment where both the luminaire control unit 410 and thecontroller 430 would be included within the luminaire 420 (either as asignal controller or as multiple units) could be particularlyadvantageous because then the luminaire 420 could then be aself-standing luminaire that can automatically adapt its dimming levelsto the presence of walls and/or distance to other luminaires in theillumination system. The illumination system 400 could then comprise aplurality of such self-standing luminaires, each of them capable ofautomatically adapt its dimming levels.

If, however, the controller 430 is not included within the luminaire420, then the luminaire 420 could include an interface (not shown inFIG. 4) configured for at least providing to the controller 430, fromthe sensor 426, information indicative of the signal strengths of thedetected back-reflected task and ambient light beams. In such anembodiment, preferably, the luminaire control unit 410 for controllingthe luminaire 420 would be included within the luminaire. Then theluminaire 420 could receive from the controller 430, via the interface,presence information indicative of whether or not objects are present inthe area surrounding the luminaire and/or information regarding distanceto other luminaires and the luminaire control unit 410 would then adjustdimming levels of the task and/or ambient light beams of the luminaire420 in accordance with that information. In this manner, the luminaire420 would be able to configure itself based, at least partially, onwhether or not the objects are present in the surrounding of theluminaire and/or the presence of and/or distance to the neighboringluminaires, as determined by the controller 430.

In the latter embodiment, each split beam luminaire within theillumination system 400 could include an associated controller such asthe controller 430, where the controller would provide instructionsregarding the dimming levels of that luminaire based on the informationdetermined by the controller for that particular luminaire (e.g. thepresence of objects in the surrounding of that luminaire or presence ofand/or distance to the neighboring luminaire from that particularluminaire). Alternatively, there could be a common system controller 430which would collect and analyze data for multiple luminaires in theillumination system 400 and then provide instructions regarding thedimming levels of individual luminaires based on the presenceinformation and/or distance information determined for differentluminaires. In this manner, a centralized control over the luminairesmay be implemented which may enable better decision-making with respectto the dimming levels of the individual luminaires in terms e.g. ofdecreased energy consumption. Further, a combination of central controlfor the some luminaires and local control for the other luminaires mayalso be possible and is within the scope of the invention.

The system controller 430 of the last embodiment may further beconfigured to acquire a lighting level configuration for the structure300, e.g. for general areas, wall areas, and/or desk areas, and tocontrol the first and second light sources of at least some of theluminaires 320 such that a total illumination pattern produced by theplurality of luminaires 320 corresponds to the lighting levelconfiguration for the structure 300. The lighting level configurationfor the structure 300 may be adjusted according to a fixed predeterminedillumination pattern or may be dependent on e.g. information regardingpresence of objects in the surrounding(s) of one or more luminairesand/or distance between the luminaires. The lighting level configurationfor the structure 300 may include not only illumination levels for thedifferent areas of the structure, but may also relate to a specificallyselected color temperature, e.g. within one or a plurality of areas ofthe structure. Dynamic adjustment is thus possible and allows forimprovements in relation to energy consumptions for the structure 300.Further sensors may be provided, either integrated or separately, andpossibly connectable to the one or more of the luminaires 320. Suchsensors may include e.g. day light detection and the system controller430 may be configured to also take such information into account whendynamically adjusting the illumination levels, locally and within thewhole structure 300.

In addition, in an embodiment, the luminaires of the illumination system400 are preferably also configured to interact wirelessly with otherluminaires in the lighting system and with the people in the room (viathe remote control 330, for example). This may be implemented byencoding information into the light beams generated by the task andambient light sources. For example, different codes included in thelight beams may be used to communicate different states (ambient/tasklighting) to neighboring luminaires in the illumination system 400, suchthat they can react accordingly, and/or the estimated distance betweenluminaire, as determined by signals received in one luminaire, can becommunicated to other luminaires and/or some central control unit of theillumination system 400.

One embodiment of the invention may be implemented as a program productfor use with a computer system. The program(s) of the program productdefine functions of the embodiments (including the methods describedherein) and can be contained on a variety of, preferably non-transitory,computer-readable storage media. Illustrative computer-readable storagemedia include, but are not limited to: (i) non-writable storage media(e.g., read-only memory devices within a computer such as CD-ROM disksreadable by a CD-ROM drive, flash memory, ROM chips or any type ofsolid-state non-volatile semiconductor memory) on which information ispermanently stored; and (ii) writable storage media (e.g., floppy diskswithin a diskette drive or hard-disk drive or any type of solid-staterandom-access semiconductor memory) on which alterable information isstored.

Even though the invention has been described with reference to specificexemplifying embodiments thereof, many different alterations,modifications and the like will become apparent for those skilled in theart. Variations to the disclosed embodiments can be understood andeffected by the skilled addressee in practicing the claimed invention,from a study of the drawings, the disclosure, and the appended claims.Further, in the claims, the word “comprising” does not exclude otherelements or steps, and the indefinite article “a” or “an” does notexclude a plurality.

1. A method for determining a distance from a sensor to a luminaire, theluminaire comprising at least a first light source configured to emit afirst light beam adapted to illuminate a predefined area and a secondlight source configured to emit a second light beam adapted toilluminate a background area surrounding the predefined area, the sensorbeing configured to detect at least a back-reflected first light beamand a back-reflected second light beam, the method comprising:determining the distance from the sensor to the luminaire based, atleast partially, on a comparison of information indicative of a firstsignal strength of the detected back-reflected first light beam andinformation indicative of a second signal strength of the detectedback-reflected second light beam.
 2. The method according to claim 1,further comprising: determining the information indicative of the signalstrength of the detected back-reflected first light beam by normalizingthe first signal strength of the detected back-reflected first lightbeam by a lumen output of the first light source, and determining theinformation indicative of the second signal strength of the detectedback-reflected second light beam by normalizing the signal strength ofthe detected back-reflected second light beam by a lumen output of thesecond light source.
 3. The method according to claim 2, wherein thecomparison of the information indicative of the first signal strength ofthe detected back-reflected first light beam and the informationindicative of the second signal strength of the detected back-reflectedsecond light beam comprises determining a ratio between the signalstrength of the detected back-reflected second light beam and the signalstrength of the detected back-reflected first light beam.
 4. The methodof claim 3, wherein the step of determining the distance from the sensorto the luminaire comprises establishing that the luminaire is aneighboring luminaire with respect to the sensor when the determinedratio is less than 1.1, preferably less than 1.0, most preferably lessthan 0.8, and, otherwise, establishing that the luminaire is along-distance luminaire with respect to the sensor.
 5. The methodaccording to claim 1, further comprising: providing an instruction toadjust a dimming level of the first light source and/or a dimming levelof the second light source based, at least partially, on the determineddistance from the sensor to the luminaire.
 6. The method according toclaim 1, wherein the first light beam comprises first data encodedtherein, the first data comprising at least an identification of thefirst light source, and the second light beam comprises second dataencoded therein, the second data comprising at least an identificationof the second light source.
 7. A controller configured for performingthe method according to claim 1, the controller configured for acquiringthe information indicative of the first signal strength of the detectedback-reflected first light beam; acquiring the information indicative ofthe second signal strength of the detected back-reflected second lightbeam; and determining the distance from the sensor to the luminairebased, at least partially, on the comparison of the informationindicative of the signal strength of the detected back-reflected firstlight beam and the information indicative of the signal strength of thedetected back-reflected second light beam.
 8. A luminaire for use in themethod according to claim 1, the luminaire comprising: the first lightsource configured for emitting the first light beam adapted toilluminate the predefined area; the second light source configured foremitting the second light beam adapted to illuminate the background areasurrounding the predefined area; an interface configured for receivinginformation indicative of the distance from the sensor to the luminaire,wherein the distance is determined based, at least partially, on thecomparison of the information indicative of the first signal strength ofthe back-reflected first light beam detected by the sensor and theinformation indicative of the second signal strength of theback-reflected second light beam detected by the sensor; and a luminairecontrol unit configured for adjusting a dimming level of the first lightbeam and/or a dimming level of the second light beam based, at leastpartially, on the received information.
 9. A second luminaire for usewith the luminaire according to claim 8, the second luminairecomprising: a third light source configured to emit a third light beamadapted to illuminate a second predefined area; a fourth light sourceconfigured to emit a fourth light beam adapted to illuminate abackground area surrounding the second predefined area; the sensorconfigured to detect at least the back-reflected first light beam andthe back-reflected second light beam; and a controller for determiningthe distance from the sensor to the luminaire based, at least partially,on the comparison of the information indicative of the signal strengthof the detected back-reflected first light beam and the informationindicative of the signal strength of the detected back-reflected secondlight beam.
 10. The luminaire according to claim 9, wherein thecontroller is further configured to: determine the informationindicative of the signal strength of the detected back-reflected firstlight beam by normalizing the first signal strength of the detectedback-reflected first light beam by a lumen output of the first lightsource, and determine the information indicative of the second signalstrength of the detected back-reflected second light beam by normalizingthe signal strength of the detected back-reflected second light beam bya lumen output of the second light source.
 11. A lighting system for astructure, comprising: a system control unit; and a plurality ofluminaires, each luminaire comprising: a first light source configuredfor emitting a first light beam adapted to illuminate a predefined area,a second light source configured for emitting a second light beamadapted to illuminate a background area surrounding the predefined area,a sensor configured for detecting at least a back-reflected first lightbeam and a back-reflected second light beam of another luminaire, and aninterface configured for providing to the system control unitinformation indicative of a signal strength of the detectedback-reflected first light beam and information indicative of a signalstrength of the detected back-reflected second light beam of the otherluminaire, wherein the system control unit is configured for: acquiringinformation detected by the sensors of at least some of the plurality ofluminaires; determining distance between at least two luminaires of theplurality of the luminaires based, at least partially, on the acquiredinformation; and controlling the first light source and/or the secondlight source of at least some of the plurality of luminaires based, atleast partially, on the determined distance.
 12. A computer programcomprising software code portion configured, when executed by aprocessor, for performing the steps according to claim
 1. 13. The methodaccording to claim 6, wherein the first data comprising informationindicative of a lumen output of the first light source, and the seconddata comprising information indicative of a lumen output of the secondlight source.